The implement may comprise a loading bucket, scoop, pallet-lifting fork, a gripping device, for instance for log-loading purposes, or a crane-arm. In the case of known linkage systems, the loader is often only intended for one single work implement, such as a bucket or a pallet-lifting fork. In this respect, it is endeavoured to move a filled bucket with the bucket constantly level, i.e. in parallelism, so as to prevent readily-pourable material from running from the bucket as it is lifted. In the case of a pallet-lifting fork, it should be possible to lift and lower the fork in parallelism, so as to prevent the load carried by the fork from sliding-off. This state of parallelism can be achieved relatively simply by adapting the system for parallel or leveling movement of a single work-implement with the tilt-cylinders locked.
U.S. Pat. No. 2,817,448 teaches a loader which is intended primarily for use with a loading bucket, where the bucket has a lower pivot-shaft on which the outer end of the lift-arm is journalled, and an upper pivot-shaft which is connected to one end of a connecting link, the other end of which link is connected to a tilt-cylinder. This, in turn, is connected to the upper lever of a two-lever shift-arm which is journalled on the lift-arm and the lower lever of which is connected by means of a link to a pivot shaft on the vehicle frame, at a location beneath the pivot-shaft of the lift-arm. The connecting link is carried by a pivot link, the upper end of which is connected to a pivot connection which is common to both the connecting link and the pivot link, and the lower end of which is pivotally connected to the lift-arm.
With linkage arrangements of this known kind it has been necessary hitherto to choose between good bucket-parallelism and a fork-parallelism which is so poor as to render it necessary to follow-up with the tilt cylinder and to adjust the length extension of the cylinder gradually so as to maintain desired parallelism, or levelling, of the fork, and vice versa when priority is given to good fork-parallelism. This gradual adjustment of the tilt-cylinder, or piston, carried out by the driver during a tilting operation, is a tiresome task.
It is known, however, that the functional characteristics of the system can be changed, inter alia by enabling the connection of the system to the vehiclechassis to be shifted from one pivot shaft to another, in the manner described in Swedish Patent Specification No. 8008328-0. This solution, however, requires considerable work to be carried out with heavy components, which may be difficult to handle on the working site.
The components forming part of a linkage system may vary in many ways, as is evident for instance, from French Patent 1,523,548, U.S. Pat. No. 4,609,322 and German LayOut Print 23 57 365, the teachings of which publications lie outside the scope of claim 1, however. These patents specifications are mentioned for the sole purpose of illustrating the many various attempts which have been made to obtain different linkage systems with different functions and characteristics.